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First of all, what is a hexapod? Hexapod is a Latin word that means “six feet”. That means a hexapod robot will consist of 6 actuators that can either be formed like a parallel arm Stewart Platform or legs like the Spider robots.
Figure 1: Hexapod Robot
The reason why hexapod robots can be used in many applications is because of the advantages they have over other types of robots. First of all, Hexapods are substantially stiffer than conventional positioning tools, more dynamic, precise, and greater in terms of flexibility. These make them more appropriate for applications requiring high degrees of accuracy, and precision.
Secondly, Hexapods are one of the best choices for high-precision applications because they provide more accurate positioning control than the other types of robots. Finally, since hexapod robots have more actuators than compared to other conventional robots they are much more stable and offer greater maneuverability.
Hexapods can vary a lot in terms of design perspective according to their intended uses. We can divide hexapod-type robots into two categories which are rectangular and hexagonal-type hexapods. Rectangular ones have rectangular-shaped bodies and two groups of three legs placed on two sides. On the other hand, hexagonal ones have circular or hexagonal-shaped bodies and legs distributed evenly. If we compare rectangular and hexagonal types we will come to the conclusion that rectangular ones are less stable and efficient.
Figure 2: Legs of the Hexapod Robot
The design purpose of the legs of these types of robots is to mimic the legs of creatures like insects. Due to the number of legs the robot’s body has, hexapods have different kinds of walking mechanisms.
Figure 4: Legs of the Hexapod Robot
This type of formation is called 3+3, in this one, we have three legs supporting the robot’s body and the other three making the movement.
Figure 5: Legs and Joints of the Hexapod Robot
While designing the hexapod-legged robots, one needs to consider a large number of possibilities. Several decisions need to be considered about the design that will have an Influence on the operation and technical features. Some of the most significant design issues and constraints are as follows:
Designing multi-axis systems can be made by serial kinematics or parallel kinematics structure. Stewart has a parallel kinematics structure. Hexapod robots sometimes referred to as the Stewart platforms consist of six actuators (arms) which are connecting 2 parts: a stationary and a moving platform.
Extending-rod style actuators are used in the legs of the Stewart Platform. These types of actuators are also referred to as “prismatic” actuators, where we can drive them by linear motors, ball screws, piezo devices, etc.
We can use Forward and Inverse kinematics methods for the calculation of the coordinate of end-effector and joint angles respectively. Inverse Kinematics is the opposite of forwarding kinematics. Sometimes the robot needs to follow a given path or locate specific coordinates, it needs to know all joint angles of all links. When the number of joints increases, the complexity of the Inverse Kinematics will increase with it.
Figure 6: Stewart Platform
Since hexapods have six actuators; they have great versatility which makes them usable in many applications such as:
Even when the placement is in relation to another moving item, precision loads may be placed precisely in many axes using hexapods based on precision ball screws, piezo motors, or voice coil actuators. As the axis of rotation is frequently outside the hexapod robot platform, this is very helpful for placing and testing semiconductor and electrical components.
Figure 7: Testing semiconductor and electrical components
In flight simulators, especially the complete flight simulator, which requires all six degrees of freedom, the Stewart platform architecture is often employed. A replica cockpit and a visual display system, typically with many channels, serve as the payload in this function and are used to show the aircraft crew in training the outside-world visual picture.
Figure 8: Flight Simulation with Stewart Platform
One of the most important applications for the Stewart platform is the hexapod-telescope which is a telescope that has a 6-DOF Stewart platform as its base instead of the typical mounting that has only 2 rotating axes. This hexapod-telescope is located at Cerros Amazones observatory located in northern Chile.
Figure 9: Telescope
Stewart Platforms are also used in stabilization applications where an object needs to be kept in a constant position against the movements of its ground plane. Satellite or radar antennas on a ship/plane, and landing platforms are ordinary objects that may need a continuous position fix to keep the position of the moving object.
Robots with legs have an advantage over those with wheels because they can climb over barriers without damaging the terrain. Fleets of autonomous-legged robots might also be used in agriculture to monitor and maintain crops without compacting the soil and endangering the crop.
Figure 10: Remote locations and hostile environments